In the process of manufacturing semiconductor devices, semiconductor elements split into individual segments from a semiconductor wafer are mounted with adhesive to a substrate such as a lead frame. The step for mounting semiconductor elements to a substrate adopted hitherto is a method in which the semiconductor elements are mounted on an adhesive material coated beforehand on the substrate. It has become difficult, however, to use the conventional method as it is, because of the advance of low-profiling of semiconductor elements in recent years.
In other words, there requires a thin layer of adhesive formed uniformly between the substrate and the semiconductor elements in order to bond the semiconductor elements properly to the substrate. When mounting thin semiconductor elements upon a surface of adhesive, however, it is difficult to press and spread the pre-coated adhesive by using rigidness of the semiconductor elements themselves since they are very flexible and low in rigidity. In addition, the adhesive tends to flow upward to upper surfaces of the semiconductor elements and stick to the mounting tool when the thin semiconductor elements are pressed upon the adhesive, thereby giving rise to a problem of impeding the normal function of the mounting tool to hold the elements.
For the above reason, there has been a tendency in recent years to adopt the method of forming an adhesive layer on semiconductor element's own surface in advance by bonding a die-attach film made of semi-cured adhesive resin in a filmily form to a semiconductor wafer before it is split into individual segments of semiconductor elements, as is disclosed, for instance, in Japanese Patent Unexamined Publication, No. 2001-185563. This technique can help reinforce the thin and flexuous semiconductor elements with the resin layer for ease of handling, and avoid drawbacks such as the adhesive flowing upward during mounting of the semiconductor elements to a substrate.
Furthermore, it requires a pressure for pressing the electronic components against the substrate and a heat for hardening the adhesive layer when securing such components as the semiconductor elements to the substrate with the adhesive layer, as disclosed in Japanese Patent Unexamined Publications, Nos. H11-135563 and H11-121508, for examples. An electronic component mounting apparatus used for the purpose of mounting semiconductor elements to the substrate is therefore equipped with a thermo-compression bonding mechanism to heat and press the semiconductor elements.
In any of the techniques illustrated in the above-referred documents for mounting semiconductor elements, however, there was a need for the semiconductor elements to be held in a state of being depressed against the substrate with a thermo-compressing tool for a predetermined duration in the process of thermo-compression bonding. This duration of holding time was not easily reducible by a large margin since it usually required a time of the order of seconds to harden the adhesive resin to a certain degree. It was thus a main factor of the difficulty in shortening the time for the mounting work, and the impediment against improving productivity of the mounting process in manufacturing the semiconductor devices.